This invention relates to an article having a large section size (i.e., about 5 inches [about 12.7 cm] in diameter or larger) made from a warm worked, austenitic, non-magnetic (i.e., magnetic permeability is less than about 1.02), stainless steel alloy. The article has high levels of strength, particularly yield strength and fatigue strength, and high levels of corrosion resistance, particularly resistance to chloride pitting, crevice corrosion and stress corrosion cracking. These properties make the article suitable for use as oilwell drilling equipment, such as a drill collar or a housing for a measurement-while-drilling (MWD) assembly, that is exposed to drilling fluid or mud. This invention also relates to an alloy with particularly high pitting resistance that renders the alloy especially suitable for making an article such as a drill collar.
Heretofore, articles such as drill collars have been prone to fail quickly in use due to cracking caused by stress corrosion and/or corrosion fatigue. The significant chloride pitting of the drill collars has been suspected to be at least partially responsible for these cracking problems.